Answer:
Let's denote the amount of calling time by "x".
For Plan A, the monthly cost would be $27 plus $0.15 per minute, so the total cost would be:
C(A) = 27 + 0.15x
For Plan B, the cost per minute is $0.19, so the total cost would be:
C(B) = 0.19x
We want to find the amount of calling time "x" for which the two plans cost the same, so we can set the two equations equal to each other and solve for "x":
27 + 0.15x = 0.19x
27 = 0.04x
x = 675
Therefore, when the amount of calling time is 675 minutes, the two plans cost the same.
To find the cost at this amount of calling time, we can substitute x = 675 into either equation:
C(A) = 27 + 0.15(675) = $121.25
C(B) = 0.19(675) = $128.25
So, at 675 minutes of calling, both plans cost the same amount, which is $121.25.